US 7060585 B1
A method utilizing in-place bonding and amorphization/templated recrystallization (ATR) is provided for making bulk and semiconductor-on-insulator substrates having coplanar semiconductor layers of different crystallographic orientations. First and second semiconductor layers having different orientations are bonded to opposite sides of a sacrificial spacer layer. Selected areas in one of the semiconductor layers are amorphized; in-place bonding is then performed in a wet etch solution to remove the sacrificial layer and leave the semiconductor layers bonded to each other. The amorphized regions are recrystallized across the bonded interface, using the semiconductor on the non-amorphized side of the bonded interface as a template.
1. A method of forming a planar hybrid orientation substrate comprising:
selecting a starting substrate comprising a first single crystal semiconductor layer having a first crystal orientation overlying a second single crystal semiconductor layer having a second crystal orientation different from the first, said first and second semiconductor layers separated by a sacrificial spacer layer;
performing a selected area amorphization on one of said first or second semiconductor layers to form localized amorphized regions in said semiconductor layer;
performing in-place bonding to bring said first and second semiconductor layers into direct contact at a bonded interface; and
recrystallizing the localized amorphized regions across the bonded interface, using the semiconductor on the non-amorphized side of the bonded interface as a template, thereby changing the orientation of the semiconductor in the localized amorphized regions from its original orientation to a desired orientation.
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18. A method of forming a planar hybrid-orientation substrate comprising:
selecting a starting substrate comprising a first single crystal semiconductor layer having a first crystal orientation overlying a second single crystal semiconductor layer having a second crystal orientation different from the first, first and second semiconductor layers separated by a sacrificial spacer layer;
replacing first single crystal semiconductor layer in selected regions with a deposited amorphous semiconductor material, thereby creating regions of deposited amorphous semiconductor material on said spacer layer;
performing in-place bonding to bring remaining regions of first semiconductor layer and regions of deposited amorphous semiconductor material into direct contact with the second semiconductor layer at a bonded interface; and
converting the deposited amorphous semiconductor material on the upper side of the bonded interface to a single crystal semiconductor material having the second crystal orientation, using a templated crystallization process wherein the underlying crystalline semiconductor layer having the second crystal orientation acts as the template.
19. The method of
This application is related to pending U.S. application Ser. No. 10/725,850, filed Dec. 2, 2003, entitled “Planar substrate with selected semiconductor crystal orientations formed by localized amorphization and recrystallization of stacked template layers,” the content of which is incorporated by reference. Likewise, this application is related to U.S. application Ser. No. 10/978,551, filed Nov. 1, 2004, entitled “In-place bonding of microstructures,” the content of which is also incorporated herein by reference.
The present invention relates to high-performance complementary metal oxide semiconductor (CMOS) circuits in which carrier mobility is enhanced by utilizing different semiconductor surface orientations for p-type field effect transistors (FETs) and n-type FETs. More particularly, the present invention relates to methods for fabricating planar substrate structures with different surface crystal orientations, and to the hybrid orientation substrate structures produced by such methods.
CMOS circuits of current semiconductor technology comprise n-type FETs (nFETs), which utilize electron carriers for their operation, and p-type FETs. (pFETs), which utilize hole carriers for their operation. CMOS circuits are typically fabricated on semiconductor wafers having a single crystal orientation. In particular, most of today's semiconductor devices are built on Si having a (100) surface orientation.
It is known that electrons have a high mobility in Si with a (100) surface orientation and that holes have a high mobility in Si with a (110) surface orientation. In fact, hole mobility can be about 2.5 times higher on a 110-oriented Si wafer than on a standard 100-oriented Si wafer. It would therefore be desirable to create hybrid orientation substrates comprising 100-oriented Si (where nFETs would be formed) and 110-oriented Si (where pFETs would be formed).
Amorphization/templated recrystallization (ATR) is one prior art approach for providing such planar hybrid orientation substrates.
It should be noted that the methods of
Like all ATR methods to date, the process flows of
A potential problem with this way of implementing ATR is that the ion implant methods typically used for amorphization leave a damaged crystalline layer between the amorphized and the non-amorphized regions of the bilayer template stack. For the case of top amorphization and bottom templating (illustrated in the process flow of
The amount of EOR damage depends somewhat on the ion implant conditions used for the amorphization. Typically, EOR damage can be reduced by implanting at low temperature (e.g., at liquid nitrogen temperature, 77K, rather than room temperature), by using heavier ions (e.g., Ge ions rather than Si ions), and with shallower implants. However EOR damage (or “beginning-of-range” damage for the case of top templating and bottom amorphization, when ion implantation is used to form a buried amorphous layer) is a characteristic of all ion implantation processes and is very difficult to avoid.
An additional difficulty with previous ATR methods of forming hybrid orientation substrates is that they require direct semiconductor-to-semiconductor (typically Si-to-Si) bonding. This is normally achieved with hydrophobic bonding, a bonding technique that is more difficult and less well developed than the more commonly used hydrophilic bonding. Hydrophobic (H-terminated) surfaces are more easily contaminated than hydrophilic ones, often leading to a choice to perform hydrophobic bonding in a vacuum environment. In addition, the widely used surface plasma treatments developed to allow room temperature bonding typically introduce surface oxygen, making them incompatible with an oxide-free bonded interface. Bonding at higher temperatures also can present difficulties, since most cleaving processes (used to separate the bonded layer from the wafer to which it was originally attached) are thermally activated and start occurring in the same temperature range as the bonding.
A new in-place bonding technique disclosed in U.S. application Ser. No. 10/978,551 provides an alternative route to the traditional direct Si-to-Si bonding described above. A basic embodiment of this technique is illustrated in
While the basic process shown in
In view of the difficulties and limitations described above, there is still a need for providing planar hybrid orientation substrates by ATR methods which (i) exploit the benefits of in-place bonding techniques, and (ii) avoid or minimize the formation of a crystalline damaged layer during the amorphization step, thereby allowing the formation of lower-defectivity hybrid orientation substrates.
The present invention provides a method of forming a hybrid orientation substrate by combining the in-place bonding methods described in U.S. application Ser. No. 10/978,551 (the content of which is incorporated herein by reference) with an ATR method which has been modified from the ATR method described in U.S. application Ser. No. 10/725,850. In the ATR method disclosed in the '850 application, selected-area amorphization was performed after formation of the bilayer template structure. In the present method, the selected area amorphization is performed before formation of the final bilayer template structure, while the upper and lower semiconductor layers are still separated by a sacrificial spacer layer. The implant energy and dose are then designed so that the highly damaged crystalline region-normally occurring at the boundary between amorphous and undamaged crystalline regions falls within the sacrificial layer, with fully amorphized semiconductor material on one side of the sacrificial layer and relatively undamaged regions of template-quality semiconductor material on the other. In-place bonding is performed after amorphization. This removes the sacrificial layer, leaving a structure in which the amorphized regions on one side of the bonded interface are in direct contact with the defect-free crystalline semiconductor material on the other.
The present method for forming hybrid orientation substrates thus incorporates the following sequence of steps to change the orientation of selected semiconductor regions from an original orientation to a desired orientation:
The basic method of the invention has two main embodiments. In the first, selected area amorphization is performed on the upper semiconductor layer and the lower layer provides the template for recrystallization. In the second (useful when the lower semiconductor layer is disposed on an insulator), the selected area amorphization is performed on the lower semiconductor layer and the upper layer provides the template for recrystallization.
With the first embodiment of top amorphization and bottom templating, amorphization can proceed without EOR damage to the substrate semiconductor layer because the EOR damage is absorbed by the sacrificial spacer layer. With the second embodiment of top templating and bottom amorphization, amorphization will leave beginning-of-range defects primarily in the sacrificial spacer layer. In both cases, the in-place bonding will leave a sharp interface between the amorphized semiconductor and the templating crystalline semiconductor, and the templating semiconductor will largely be free of defects. If desired, some annealing may be performed prior to in-place bonding to heal beginning-of-range defects in the upper semiconductor layer, and/or to slightly densify the amorphized regions. While the conditions for this pre-crystallization annealing must be mild enough to avoid spontaneous crystallization of the amorphized regions, there is no problem with annealing at the lower (but still elevated) temperatures at which templated recrystallization would occur, since amorphized and templating layers are not yet in direct contact.
This basic method may be adapted in whole or in part to form planar hybrid orientation semiconductor structures on a variety of substrates or substrate layers, including bulk semiconductors, thin or thick insulating layers, and insulating (or high resistivity) substrates. Different planar hybrid orientation substrates will typically require different starting substrates. Single layer semiconductor-on-insulator (SOI) substrates would typically be the starting substrates for forming a bulk planar hybrid orientation substrates, whereas a double layer SOI substrate would typically be the starting substrate for forming a SOI planar hybrid orientation substrate.
It should be noted that the hybrid orientation substrates provided by the methods of this invention are referred to as planar because the top surfaces of differently oriented semiconductor regions lie in the same horizontal plane. True planarity would typically be achieved by depositing one or more insulating layers on the “planar” hybrid orientation substrate to fill and overfill any topography, and then planarizing by a process such as chemical mechanical polishing (CMP).
As discussed above in connection with the description of the prior art ATR methods, additional processing steps may be incorporated into the basic method to minimize the possibility of lateral templating. In addition, “Separation by Implantation of Oxygen” (SIMOX) processes such as those described in U.S. application Ser. No. 10/725,850 and U.S. application Ser. No. 10/902,557, “Dual SIMOX hybrid orientation technology (HOT) substrates,” may be used to create buried insulating layers (or thicken existing buried insulator layers) in the planar hybrid orientation substrates created by the methods of this invention to produce hybrid orientation SOI substrates. Other additional processing steps and variations (for example, utilizing various hard mask layers that may be removed before or after bonding, and/or before or after implantation; extension of the method to more than two orientations) may also be added without departing from the basic method of the invention.
In another embodiment of the invention, a layer comprising crystalline semiconductor regions having a first crystal orientation and amorphous semiconductor regions is formed on top of a sacrificial layer disposed on an underlying semiconductor having a second crystal orientation. After in-place bonding, the amorphous regions are converted into crystalline regions having the crystal orientation of the underlying semiconductor.
In a variation of this embodiment, a layer comprising single crystal semiconductor regions of a first semiconductor material and amorphous semiconductor regions of a second semiconductor material is formed on top of a sacrificial layer disposed on an underlying single crystal semiconductor of the second semiconductor material. After in-place bonding, the amorphous regions are converted into single crystal regions having crystal orientation of the underlying semiconductor.
It is envisioned that the hybrid orientation substrates produced by the methods of this invention would be further processed with methods known in the art to form planar hybrid orientation substrates with semiconductor devices and/or integrated circuits thereupon.
These and other features, aspects, and advantages will be more readily apparent and better understood from the following detailed description of the invention, in which:
The present invention, which provides methods of fabricating planar hybrid-orientation substrate structures, will now be described in greater detail by referring to the drawings that accompany the present application. The drawings that accompany the present application are provided for illustrative proposes and thus they are not drawn to scale. In the drawings, which illustrate the process flows of the present invention, reference numbers are not shown for materials (or areas) that are not be affected by the specified processing step. It is understood then that the materials not labeled in a particular step have not changed from the proceeding step(s). Also, in the drawings, like and/or corresponding materials are described with like reference numerals.
As mentioned above, the methods of the present invention share the following basic steps of: selecting a starting substrate comprising a first single crystal semiconductor layer having a first crystal orientation overlying a second single crystal semiconductor layer having a second crystal orientation different from the first, wherein the first and second semiconductor layers are separated by a sacrificial spacer layer; amorphizing selected areas of first or second semiconductor layer (by ion implantation through a mask, for example) to form localized amorphized regions; using an in-place bonding process to bring first and second semiconductor layers into direct contact at a bonded interface; and recrystallizing the localized amorphized regions across the bonded interface, using the semiconductor on the non-amorphized side of the bonded interface as a template, thereby changing the orientation of the semiconductor in the localized amorphized regions from its original orientation to a desired orientation.
One or more features 390 are then subjected to ion bombardment (typically ion implantation) 400 to create amorphized semiconductor features 410, as shown in
The progression of in-place bonding/sacrificial spacer layer removal (typically performed in an aqueous solution containing hydrofluoric acid) is shown in
If desired, amorphized semiconductor features 410 may be annealed prior to the in-place bonding to improve their resistance to the etching solution used for removal of the sacrificial spacer layer. The annealing may be performed under any time/temperature conditions that do not lead to spontaneous recrystallization (i.e., non-templated recrystallization into polycrystalline material). Since the amorphized material is not in contact with a templating semiconductor surface, the allowable conditions include those at which one would ordinarily see rapid templated recrystallization.
The structure of
While it is preferred that the dielectric fill/overfill and planarization steps be performed after the recrystallization step shown in
The patterning of layer 360 (with or without amorphized regions 360′) would typically be performed by forming and then etching through a patterned mask, using a process such as reactive ion etching (RIE). This etch is shown in
The process steps required to complete the structure of
For certain device applications, however, it would be desirable to have planar SOI hybrid orientation substrates rather than planar bulk hybrid orientation substrates.
One or more features 610 are then subjected to ion bombardment (typically ion implantation) 620 to create amorphized semiconductor features 630, as shown in
The progression of in-place bonding/sacrificial spacer layer removal, analogous to the steps of
The structure of
As described earlier in this section, the exact sequence of steps is typically not critical. If desired, the dielectric fill/overfill and planarization steps may be performed prior to the recrystallization step, though preferably not before removal of exposed regions 680 of lower semiconductor 570. Variations such as those described in
A potential drawback of the
Residual bonded semiconductor-to-semiconductor interface 700 is avoided in a “bottom amorphization/top templating” version of the present invention, as shown in
One or more features 610 are then subjected to ion bombardment (typically ion implantation) 720 to create buried amorphized semiconductor regions 730 and slightly damaged semiconductor features 610′, as shown in
The progression of in-place bonding/sacrificial spacer layer removal, analogous to the steps of
There are several ways to get from the structures of
Alternatively, one could get to the structure of
Maskless RIE, selective to underlying insulator layer 590, is a simple, though possibly damaging method for producing the structure of
The present invention also provides a variation of the above-described “top amorphization/bottom templating” method for forming planar hybrid orientation substrates. In this variation, no selected area amorphization steps are required. The steps of this “deposited amorphous/bottom templating” method comprise: selecting a starting substrate comprising a first single crystal semiconductor layer having a first crystal orientation overlying a second single crystal semiconductor layer having a second crystal orientation different from the first, first and second semiconductor layers separated by a sacrificial spacer layer; replacing first single crystal semiconductor layer in selected regions with a deposited amorphous semiconductor material, thereby creating regions of deposited amorphous semiconductor material on said spacer layer; using an in-place bonding process to bring remaining regions of first semiconductor layer and regions of deposited amorphous semiconductor material into direct contact with the second semiconductor layer at a bonded interface; and converting the deposited amorphous semiconductor material on the upper side of the bonded interface to a single crystal semiconductor material having the second crystal orientation, using a templated crystallization process wherein the underlying crystalline semiconductor layer having the second crystal orientation acts as the template.
Crystalline semiconductor features 610 and amorphous semiconductor feature 810′ are then bonded to SOI layer 570 by in-place bonding, as shown in
The method discussed in
As described in connection with the other process flows of this invention, the exact sequence of certain steps is frequently not critical. Variations such as those described in
When choosing a process flow and starting substrate structure, it should be kept in mind that different semiconductor orientations can have different recrystallization rates as well as different defect levels in the recrystallized material. The orientation into which the amorphized or amorphous regions will be transformed is preferably selected to be the one which has the easiest growth and lowest defectivity. With this approach, the layer with the easier-to-recrystallize orientation provides the template layer; some regions of the semiconductor layer with the harder-to-recrystallize orientation would keep their original orientation, while others would be amorphized (or replaced with amorphous semiconductor material) and converted into the easier-to-recrystallize orientation. For the case of Si, it would thus be preferable to convert selected regions of 110-oriented Si into 100-oriented Si rather than the reverse.
The substrates and single crystal semiconductor layers of the present invention may be selected from a wide range of semiconductor materials. For example, substrate 600 (if a semiconductor) and differently oriented first and second semiconductor layers 360, 370, 560, and 570 may be selected from the group including Si, SiC, SiGe, SiGeC, Ge alloys, Ge, C, GaAs, InAs, InP as well as other III–V or II–VI compound semiconductors. Layered combinations or alloys of the aforementioned semiconductor materials (for example, Si layers on SiGe), with or without one or more dopants, are also contemplated herein. First and second semiconductor regions may be strained, unstrained, or a combination of strained and unstrained layers can be used. For Si-containing semiconductor layers, the crystallographic orientations would typically be selected from the group including (110), (111), and (100). Preferred choices of first and second semiconducting layer for the structures of
The thickness of first and second single crystal semiconductor regions 360, 560, and 570 is typically from about 1 to about 500 nm, with a thickness from about 10 to about 100 nm being more typical. The thickness of semiconductor layer 370 and substrate 600 would typically be between 5 and 1000 μm, and most typically be about 600 μm.
Buried insulator layer 590 (and substrate 600, if insulating) may be selected from a wide range of dielectric materials, including, but not limited to the group including SiO2, crystalline SiO2, SiO2 containing nitrogen or other elements, silicon nitrides, metal oxides (e.g., Al2O3), insulating metal nitrides (e.g., AlN), highly thermally conductive materials such as crystalline diamond. Buried insulating thicknesses may range from about 2 nm to about 500 nm, with preferable thicknesses typically being in the range from about 50 to about 150 nm.
Starting substrate structures (e.g., substrate structures 350 of
As discussed in U.S. application Ser. No. 10/725,850, selected area amorphization would typically be effected by ion implantation. The optimum ion implantation conditions, the species, ion energy, dose, tilt and twist angle, temperature, number and sequence of implants, etc. will depend on the structure of the starting substrate, the materials and thicknesses of the semiconductor layers, and the position (upper or lower) of the semiconductor layer being amorphized. Any ion species known to those skilled in the art may be used for the amorphization. Typically the implanted species would comprise at least one element selected from the group including but not limited to: Si, Ge, Ar, C, O, N, H, He, Kr, Xe, P, B, As, and the like. Si or Ge are preferred implantation species when Si is the semiconductor material being amorphized. Lighter ions such as H and He are typically less effective at amorphization. Ion implantation may be performed at temperatures ranging from cryogenic (77K or lower) to several hundred degree Celsius (e.g., 500° C.). However, it should be noted that the implant dose required for amorphization increases with temperature, and that implantation temperatures below 50° C. would typically be preferred for all “top amorphiztion/bottom templating” process flows.
Regions not being amorphized would typically be protected from ion implantation by a patterned mask (for example, a patterned photoresist for a room temperature implantation process). Implants may be performed with or without “screen oxide” layers and may be performed with multiple implants at different energies if a sufficiently uniformly amorphized region cannot be easily achieved with a single implant. For example, Si implanted at cryogenic temperatures at 50, 100, 150, and 200 keV with a total dose of 6E15/cm2 was found to be sufficient to amorphize the top 400 nm of 100-oriented and 110-oriented Si. See, for example, L. Csepregi et al., J. Appl. Phys. 49 3096 (1978). However, much lower doses (for example, 5E14/cm2 at 40 keV) can amorphize Si when the implanted ion is Ge and surface region to be amorphized is thinner than 50–100 nm.
As discussed in U.S. application Ser. No. 10/725,850, recrystallization of localized amorphous regions is typically effected by annealing at temperatures from about 200° to about 1300° C., preferably from about 400° to about 900° C., and more preferably from about 450° and 650° C., for a time period sufficient to bring about the desired recrystallization. This time period will depend on the orientation of the template layer, on the thickness of the amorphized region to be recrystallized, and on the presence of implanted and other impurities in the amorphized layer. Annealing may be performed in a furnace or by rapid thermal annealing. In other embodiments, annealing may be performed using a laser anneal or a spike anneal. The annealing ambient would typically be selected from the group of gases including N2, Ar, He, H2 and mixtures containing any of these gases. Additional post-recrystallization anneals (typically at the high end of the temperature range mentioned above) may also be performed after the initial recrystallization anneal to reduce the defectivity and/or improve the quality of the recrystallized material.
Any conventional combination of ion implantation and annealing steps may be employed following recrystallization to create a buried insulator layer (or to extend an existing buried insulator layer). For example, any conventional SIMOX process can be used to add a buried oxide layer to the structures shown in
FET devices of
While the present invention has been particularly shown and described with respect to preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in forms and details may be made without departing from the spirit and scope of the present invention. It is therefore intended that the present invention not be limited to the exact forms and details described and illustrated, but fall within the scope of the appended claims.